Evaluation of column hardware on liquid chromatography–mass spectrometry of phosphorylated compounds

Study of retention and peak shape in hydrophilic interaction chromatography over a wide pH range

“…It appears that some ions can be specifically adsorbed, inducing considerable shifts in pzc, whereas other ions are not specifically adsorbed (so-called "inert" electrolytes) and are adsorbed by electrostatic forces. The values of pzc in these reports [26][27][28][29] are consistent with the possibility that the silica matrix has an overall positive charge in TFA/HFBA mobile phases, at least in the BEH amide and bare silica columns studied in this work.…”

“…Neither of these effects could occur with bare silica phases. Metal ions that originate from the column hardware, especially the frits, could be responsible for the presence of positive charges on the surface [26]. Experiments in which the metal complexing agents acetylacetone or EDTA were incorporated into the mobile phase however, did not indicate any appreciable effects, although EDTA is rather insoluble in HILIC mobile phases and had to be used in concentrations < 1mM.…”

Retention characteristics of some antibiotic and anti-retroviral compounds in hydrophilic interaction chromatography using isocratic elution, and gradient elution with repeatable partial equilibration

“…Carr et al [40] showed that corrosion of stainless steel column frits in acidic mobile phases results in the release of metal-oxides such as iron(II)/iron(III). Also, it has been shown elsewhere [41] that replacement of stainless steel frits with polyethylene-type were beneficial for the RP chromatography of metal-chelating phosphorylated compounds. It is therefore likely that available metal oxides become immobilised on silanol groups and thus act as metal affinity exchange sites.…”

Some factors that can lead to poor peak shape in hydrophilic interaction chromatography, and possibilities for their remediation

“…Some manufacturers supply biocompatible systems that are supposed to be inert to such interactions, using alternative material to steel where possible [24,25]. Elsewhere [26], it has been shown that replacement of stainless steel with polyethylene frits could be beneficial for improving peak shapes of phosphorylated compounds in RP chromatography. This is important since it has also been shown [23] that the corrosion of stainless steel frits in the presence of acidic mobile phases results in the release of metal-oxides such as Fe 2+ /Fe 3+ .…”